PERFORMANCE CONNECTING RODS
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PERFORMANCE CONNECTING RODS |
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Performance Connecting Rods
Aluminum
Aluminum rods are manufactured by the forging process, or they can be cut from a sheet of aluminum plate, billet-style. Aluminum rods are generally 25- percent lighter than steel rods, and for this reason they’re very popular with racers looking to shed mass from the reciprocating assembly. Lighter reciprocating parts demand less energy to set into motion, allowing more of the force of combustion to be applied to the wheels. Lower reciprocating mass also allows the engine to gain crank speed faster for quicker rpm rise after each up shift, to keep the engine near the peak of the power curve. That’s the good news.
The downside is that aluminum has a much shorter fatigue life than steel, perhaps one-tenth as long in a racing environment. This means you’ll have to measure for stretch and replace suspect rods at regular intervals to stay ahead of possible catastrophic failure. How long will they go? That depends on how hard they’re loaded and if they’re abused. We’ve all heard stories about hot rodders getting 100,000 street miles out of a set of aluminum rods. Could be. But the fact remains that aluminum has a tendency to work-harden with use. Going back to the analogy of the coat hanger, if you keep twisting it, it’ll break. That’s work hardening, and an aluminum coat hanger can’t handle the same strain for nearly as long as a hypothetical steel coat hanger.
Another hassle is the fact that aluminum rods must be made physically larger because the ultimate tensile strength is about half that of a good steel rod. The added bulk often causes clearance problems inside the crankcase, especially when they’re swinging from a stroker crank. Some aluminum rod users abuse them without even knowing it. A cold motor must be warmed thoroughly because the expansion rate of aluminum is twice that of steel. The difference in expansion between the steel crank pin and aluminum big end can restrict the oil film clearance until the temperature of all parts stabilizes. Wing the throttle on an ice-cold motor, and you might be looking at spun rod bearings, or worse.
Aluminum rods can handle plenty of horsepower. You’ll want to check with the manufacturer for specifics, but it is safe to say that 2 horsepower per cubic inch is just the beginning. We’ll err on the side of caution and say that aluminum rods are best suited to race-only engines where regular inspection can ward off potential trouble.
Titanium
Got a huge wad of cash burning a hole in your wallet? Then you’ll want to know that titanium rods offer the highest strength-to-mass ratio of them all. A well-designed titanium rod is about 20 percent lighter than a comparable steel rod. Titanium is the most abundant element in the earth’s crust, but it must be alloyed with other metals before it has the properties needed for the manufacture of connecting rods. The most common alloy is called “Titanium 6-4” because it has 6 percent aluminum and 4 percent vanadium to improve machine ability.
Like steel and aluminum rods, titanium rods can be forged or cut from a billet.
Given a choice, titanium rods are most durable when manufactured by the
forging process. This is because the grain size of even the best aerospace
grade titanium is less than steel. In a Richter-esque grain-sizing scale
where a 6 rating is twice as tight as a 5 rating, titanium rates between
5 and 6 while high-carbon steel is far more cohesive, rating as high as
a 9. To offset the possible negative impact on strength, a fully machined
forged titanium rod is the best type thanks to the improved grain structure
around the big end versus a cut-out true billet titanium rod.
Though raw titanium costs five times as much as raw carbon steel, the average
retail cost of a set of titanium rods is “only” about twice that
of steel. The increased consumer cost reflects the fact that titanium becomes “gummy” when
machined and requires specialized tooling and slower feed rates. Titanium
expands at about the same rate as steel and is resistant to work hardening,
so you could run ’em in your street car with no problems as long as
your wife never sees the credit card bill. So where do titanium rods really
shine? In any all-out racing effort where an approximate 15-percent reduction
in ultimate tensile strength is an acceptable trade-off for an approximate
20-percent reduction in connecting rod weight. As for ultimate power capacity,
know that they’re used in everything from 9,000-rpm NASCAR motors to
a handful of 6,000hp Top Fuel motors (though most teams use aluminum). With
the right communication between you and the manufacturer, they’ll handle
anything you can throw at ’em. Just be sure not to scratch them! Titanium
is very “notch sensitive.” Small surface imperfections caused
by rough handling must be polished immediately, or they can grow quickly.
Call 1-877-354-3812 to order your Connecting Rods Today!!